I dont think he completed the challenge. He found a loophole, so _maybe_ you could say he was successful. In exploiting the rules that is, not in solving the problem that Goldman stated. Still a clever solution, but obviously not what was asked for.
Every technique is "just a loophole" when it's first discovered.
I'm sure Rivest, Shamir, and Adleman would disagree. So would Lempel and Ziv.
But he didnt actually succeed in getting the desired result- the problem was that the statement of the problem was flawed. There obviously is a difference between what Goldstein meant, and what he said.